Visual and quantitative lateral flow immunoassay based on Au@PS SERS tags for multiplex cardiac biomarkers.

Rapid and sensitive detection of multiple biomarkers by lateral flow immunoassay (LFIA) remains challenging for signal amplification for commonly used nanotags. Herein, we report a novel LFIA strip for visual and highly sensitive analysis of two cardiac biomarkers based on functionalized gold nanoparticles @ polystyrene microsphere (Au@PS）microcavity as surface-enhanced Raman scattering (SERS) tags. Antibody-modified Au@PS was designed as a SERS label. The evanescent waves propagating along the surface of the PS microcavity and the localized surface plasmons of the gold nanoparticles were coupled to enhance the light-matter interaction synergistically for Raman signal enhancement. In this strategy, the proposed Au@PS SERS tags-based LFIA was carried out to quantify the content of the heart failure and infarct biomarkers synchronously within 15 min and get the limits of detection of 1 pg/mL and 10 pg/mL for cardiac troponin I (cTnI) and N-terminal natriuretic peptide precursor (NT-proBNP), respectively. The results demonstrated 10-20 folds more sensitivity than that of the standard colloidal gold strip and fluorescent strip for the same biomarkers. This novel quantitative LFIA shows promise as a high-sensitive and visual sensing method for relevant clinical and forensic analysis.

Construction of a microcavity-based microfluidic chip with simultaneous SERS quantification of dual biomarkers for early diagnosis of Alzheimer's disease.

Since there is no effective Alzheimer's disease (AD)-modifying therapy available currently, early analysis of AD core biomarkers has become one of great significance and common concern in clinical diagnosis. Herein, we designed an Au-plasmonic shell attached polystyrene (PS) microsphere in a microfluidic chip for simultaneous detection of Aß1-42 and p-Tau181 protein. The corresponding Raman reporters were identified in femto gram level by ultrasensitive surface enhanced Raman spectroscopy (SERS). Both of Raman experimental data and finite-difference time-domain modeling demonstrates the synergetic coupling between PS microcavity with the optical confinement property and the localized surface plasmon resonance (LSPR) of AuNPs, so leading to highly amplified electromagnetic fields at the 'hot spot'. Moreover, the microfluidic system is designed with multiplex testing and control channels in which the AD-related dual proteins were detected quantitatively with a lower limit of 100 fg mL-1. Thus, the proposed microcavity-based SERS strategy initiates a new way for accurately prediction of AD in human blood samples and provides the potential application for synchronous determination of multiple analytes in general disease assays.

Hydrophilic polypyrrole and g-C3N4 co-decorated ZnO nanorod arrays for stable and efficient photoelectrochemical water splitting.

It is of practical significance to manufacture high-performance and durable semiconductor heterojunctions for photoelectrochemical (PEC) water splitting. Herein, hydrophilic polypyrrole and graphitic carbon nitride (g-C3N4) co-decorated ZnO nanorod arrays were synthesized as a photoanode by facile spin-coating and plasma-treatment methods. On the one hand, g-C3N4 nanosheets are modified on ZnO nanorod arrays to broaden the light-absorption range and suppress the recombination of photogenerated charges. On the other hand, the polypyrrole coating layer inhibits the dissolution and corrosion of ZnO nanorods and constructs a p-n heterojunction with ZnO to further promote the separation and transfer of photogenerated charge carriers. Furthermore, its hydrophilic surface provides a vast electrochemically active surface area for efficient charge/mass transfer. As a result, the as-prepared photoanode exhibits an enhanced PEC performance with a distinctly increased photocurrent and remarkably ameliorated stability in contrast to the ZnO photoanode. This research would provide an innovative perspective on the design of organic/inorganic semiconductor heterojunctions with excellent performance and stability for PEC water-splitting systems.

Label-Free Sensing of Biomolecular Adsorption and Desorption Dynamics by Interfacial Second Harmonic Generation.

Observing interfacial molecular adsorption and desorption dynamics in a label-free manner is fundamentally important for understanding spatiotemporal transports of matter and energy across interfaces. Here, we report a label-free real-time sensing technique utilizing strong optical second harmonic generation of monolayer 2D semiconductors. BSA molecule adsorption and desorption dynamics on the surface of monolayer MoS2 in liquid environments have been all-optically observed through time-resolved second harmonic generation (SHG) measurements. The proposed SHG detection scheme is not only interface specific but also expected to be widely applicable, which, in principle, undertakes a nanometer-scale spatial resolution across interfaces.

Plasmon-exciton coupling dynamics and plasmonic lasing in a core-shell nanocavity.

Plasmonic nanolasers based on the spatial localization of surface plasmons (SPs) have attracted considerable interest in nanophotonics, particularly in the desired application of optoelectronic and photonic integration, even breaking the diffraction limit. Effectively confining the mode field is still a basic, critical and challenging approach to improve optical gain and reduce loss for achieving high performance of a nanolaser. Here, we designed and fabricated a semiconductor/metal (ZnO/Al) core-shell nanocavity without an insulator spacer by simple magnetron sputtering. Both theoretical and experimental investigations presented plasmonic lasing behavior and SP-exciton coupling dynamics. The simulation demonstrated the three-dimensional optical confinement of the light field in the core-shell nanocavity, while the experiments revealed a lower threshold of the optimized ZnO/Al core-shell nanolaser than the same-sized ZnO photonic nanolaser. More importantly, the blue shift of the lasing mode demonstrated the SP-exciton coupling in the ZnO/Al core-shell nanolaser, which was also confirmed by low-temperature photoluminescence (PL) spectra. The analysis of the Purcell factor and PL decay time revealed that SP-exciton coupling accelerated the exciton recombination rate and enhanced the conversion of spontaneous radiation into stimulated radiation. The results indicate an approach to design a real nanolaser for promising applications.

Inhomogeneous Trap-State-Mediated Ultrafast Photocarrier Dynamics in CsPbBr3 Microplates.

Quantitatively elucidating photocarrier dynamics mediated by trap states in perovskites is crucial for establishing a structure-performance relation and understanding the interfacial photocarrier transport mechanism. Here, trap-state-mediated photocarrier dynamics in defect-rich CsPbBr3 microplates are noninvasively investigated by ultrafast laser spectroscopy. Time-resolved photoluminescense (TRPL) measurements as a function of sample thickness indicate that trap densities of surface and bulk regions are inhomogeneous, leading to fast and slow decay components of TRPL, respectively. Fast and slow PL lifetimes present the same decreasing trend as the thickness is decreased from 5 to 0.1 µm, suggesting that both surface and bulk trap densities dramatically increase in sub-micrometer thick microplates. Furthermore, dynamical competition of ultrafast photocarrier energy relaxations between surface and bulk regions is studied in a 1.6 µm-thick sample by temporally correlating pump fluence-dependent TRPL with transient absorption signals. Strikingly, long-lived hot carriers (20 ps) are observed and complete filling of mid-gap trap states in the surface region can markedly enhance PL emission in the bulk region. By control measurements, we attribute these anomalous phenomena to the polaron-assisted ultrafast energy transfer process across the surface-bulk interface. Our results provide new insights into dynamical photocarrier energy relaxations and interfacial energy transport for inorganic perovskites.

CdS quantum dots/Au nanoparticles/ZnO nanowire array for self-powered photoelectrochemical detection of Escherichia coli O157:H7.

In this paper, the hydrothermally grown ZnO nanowire array (NWs) was modified by Au nanoparticles (NPs) and CdS quantum dots (QDs) to construct a high-performance photoelectrochemical (PEC) electrode. The aligned ZnO NWs, which decorated Au NPs and CdS QDs have the effective light absorption range from UV to visible region. This hybrid structure provided a self-powered PEC electrode with a favorable energy-band configuration for fast charge separation and transportation. Meanwhile, the Au NPs and CdS QDs also made increase of the surface area to improve the immobilization of the analytes. After assembling aptamer as recognition element, this composite nanoarray was further developed as a self-powered PEC biosensor by synergizing above multiple enhancement factors. The PEC aptasensor exhibited a rapid response in a wide linear range of 10-107 CFU/mL with the detection limit as low as 1.125 CFU/mL to Escherichia coli O157:H7 (E. coli O157:H7). This approach would offer an alternative PEC transduction for fast environment monitoring and clinical diagnosis related to pathogenic bacteria.

Bilinear Staphylococcus aureus detection based on suspension immunoassay.

A novelty bilinear suspension immunoassay biosensor is developed for Staphylococcus aureus specific detection. In the present study, a dual-color-based sandwich immunosensor was constructed for sensitive and selective detection of this bacterium. In this bioassay system, the monoclonal antibodies of Staphylococcus aureus were immobilized on carboxyl-modified fluorescent microspheres (PSA-R6G) which acted as a capture probe. A secondary fluorescein isothiocyanate (FITC)-labelled antibody of Staphylococcus aureus acted as a sensitive reporter antibody. After dual-labelling with R6G and FITC, the enriched Staphylococcus aureus bacteria were observed by using the multiparameter flow cytometry analysis. In this method, two regression equations were obtained with IFITC = 1.56lgC + 4.50 and IR6G = 1.54lgC + 2.78, respectively. It can be noted that the two slopes were very similar, which indicated the false positives decrease significantly. For general applications, the quantificational measurements of Staphylococcus aureus in milk and water samples were also carried out. The suspension immunoassay exhibited an excellent specificity to Staphylococcus aureus in contrast to conventional culture-based method.

Self-Assembled Growth of Ultrastable CH3NH3PbBr3 Perovskite Milliwires for Photodetectors.

The unstability of organolead halide perovskite under continuous illumination, moisture, and high temperature has seriously impeded its commercial development for long-period applications. Here, a facile method was developed to grow ultrastable CH3NH3PbBr3 milliwires through the reaction of self-assembled PbBr2 milliwire with CH3NH3Br at room temperature. The initial self-assembled PbBr2 milliwire is that PbBr2 complexed with dimethylformamide (DMF) molecular self-assemble into perovskite-type PbBr2. Crystal conversion from PbBr2 to CH3NH3PbBr3 milliwire occurred in the molecular exchange between CH3NH3Br and DMF. The synthesized CH3NH3PbBr3 milliwires present high stability under high humidity ∼75%, continuous illumination, heating, and sustain ultrastability in air for more than 255 days. In addition, the CH3NH3PbBr3 milliwire can be dynamically degraded and reconstructed in the presence of water molecules. The milliwires have strong band-edge photoluminescence (PL) with PL lifetime of ∼110 ns. On the basis of the mono-milliwire-constructed photodetector, it exhibits high photoresponse and fast response time of 0.407 s.

Dual functional NaYF4:Yb3+, Er3+@NaYF4:Yb3+, Nd3+ core-shell nanoparticles for cell temperature sensing and imaging.

Lanthanide-doped up-conversion nanoparticles (UCNPs) provide a remote temperature sensing approach to monitoring biological microenvironments. In this research, the UCNPs of NaYF4:Yb3+, Er3+@NaYF4:Yb3+, Nd3+ with hexagonal (ß)-phase were synthesized and applied in cell temperature sensing as well as imaging after surface modification with meso-2, 3-dimercaptosuccinic acid. In the core-shell UCNPs, Yb3+ ions were introduced as energy transfer media between sensitizers of Nd3+ and activators of Er3+ to improve Er3+emission and prevent their quenching behavior due to multiple energy levels of Nd3+. Under the excitations of 808 nm and 980 nm lasers, the NaYF4:Yb3+, Er3+@NaYF4:Yb3+, Nd3+ nanoparticles exhibited an efficient green band with two emission peaks at 525 nm and 545 nm, respectively, which originated from the transitions of 2H11/2 â†’ 4I15/2 and 4S3/2 â†’ 4I15/2 for Er3+ ions. We demonstrate that an occurrence of good logarithmic linearity exists between the intensity ratio of these two emission peaks and the reciprocal of the inside or outside temperature of NIH-3T3 cells. A better thermal stability is proved through temperature-dependent spectra with a heating-cooling cycle. The obtained viability of NIH-3T3 cells is greater than 90% after incubations of about 12 and 24 (h), and they possess a lower cytotoxicity of UCNPs. This work provides a method for monitoring the cell temperature and its living state from multiple dimensions including temperature response, cell images and visual up-conversion fluorescent color.

Burstein-Moss Effect Behind Au Surface Plasmon Enhanced Intrinsic Emission of ZnO Microdisks.

In this paper, ZnO microdisks with sputtering of Au nanoparticles were prepared to explore their plasmon/exciton coupling effect. An obvious blue shift and enhanced excitonic emission intensity were observed in the PL spectra of as-grown and Au-sputtered ZnO samples at room temperature. The investigation on the absorption spectra and temperature-dependent PL spectra has been demonstrated the Burstein-Moss effect behind the optical phenomena. These results revealed the coupling dynamics between the metal localized surface plasmon and semiconductor exciton.

Plasmon-enhanced Electrically Light-emitting from ZnO Nanorod Arrays/p-GaN Heterostructure Devices.

Effective and bright light-emitting-diodes (LEDs) have attracted broad interests in fundamental research and industrial application, especially on short wavelength LEDs. In this paper, a well aligned ZnO nanorod arrays grown on the p-GaN substrate to form a heterostructured light-emitting diode and Al nanoparticles (NPs) were decorated to improve the electroluminescence performance. More than 30-folds enhancement of the electroluminescence intensity was obtained compared with the device without Al NPs decoration. The investigation on the stable and transient photoluminescence spectraof the ZnO nanorod arrays before and after Al NPs decoration demonstrated that the metal surface plasmon resonance coupling with excitons of ZnO leads to the enhancement of the internal quantum efficiency (IQE). Our results provide aneffective approach to design novel optoelectronic devices such as light-emitting diodes and plasmonic nanolasers.

Green emission and Ag(+) sensing of hydroxy double salt supported gold nanoclusters.

In this paper, a complex of Zn-containing hydroxy double salt (Zn-HDS) supported gold nanoclusters (AuNCs) has been synthesized. The formation of the complex (denoted as the AuNCs/Zn-HDS complex) has been analyzed by Transmission Electron Microscopy (TEM), IR spectroscopy and X-ray Photoelectron Spectroscopy (XPS). It is noteworthy that the AuNCs/Zn-HDS complex emits green fluorescence and the quantum yield is 7.6%. Based on the fluorescence quenching effect, the AuNCs/Zn-HDS complex has been employed for the sensitive detection of Ag(+) and the limit of detection is 2.32 nM. The mechanisms of fluorescence generation and quenching are discussed in detail.

Facile synthesis of highly conductive sulfur-doped reduced graphene oxide sheets.

A facile hydrothermal strategy to synthesize sulfur-doped reduced graphene oxide (S-RGO) sheets with good conductivity is proposed by using only graphene oxide (GO) sheets and sodium sulphide (Na2S) as precursors through a hydrothermal reaction process at 200 °C in one pot. The introduced Na2S can act as not only a sulfur dopant, but also as a highly efficient reducing agent in the formation of S-RGO sheets, which dramatically improves the electrical conductivities of the resulting S-RGO sheets compared with previous reports. The current reaches about 50.0 mA at an applied bias of 2.0 V for the optimized sample with 2.22 at% sulfur doping. This current value is much higher than that of RGO sheets (∼1.2 mA) annealed at 200 °C, and very close to that of single-layer graphene sheets (∼68.0 mA) prepared using chemical vapor deposition under the same test conditions. The resulting highly conductive S-RGO sheets offer many promising technological applications such as efficient metal-free electrocatalysts in oxygen reduction reactions in fuel cells and as supercapacitor electrode materials for high-performance Li-ion batteries.

Ultrasonication-Assisted Controllable Self-Assembly of Graphene Oxide.

A facile, and cost-efficient ultrasonication-assisted exfoliation strategy is proposed to fabricate GO sheets with various sizes. Just by controlling the original GO sizes as basic building blocks in deionized water, various aligned architectures, such as films, microfibers, submicron rods, and nanorods, are self-assembled at the water/air interface. The formation mechanisms are analyzed on the basis of the morphology evolutions of various aligned architectures. It is very interesting to note that various functional structures are generally aligned in a certain direction, which is probably attributed to the intrinsic lamellar orientation and the corresponding polarity of the GO sheets. This work provides a beneficial reference for controlling the assembling behaviors of GO in a broad range of applications.

Single Mode ZnO Whispering-Gallery Submicron Cavity and Graphene Improved Lasing Performance.

Single-mode ultraviolet (UV) laser of ZnO is still in challenge so far, although it has been paid great attention along the past decades. In this work, single-mode lasing resonance was realized in a submicron-sized ZnO rod based on serially varying the dimension of the whispering-gallery mode (WGM) cavities. The lasing performance, such as the lasing quality factor (Q) and the lasing intensity, was remarkably improved by facilely covering monolayer graphene on the ZnO submicron-rod. The mode structure evolution from multimodes to single-mode was investigated systematically based on the total internal-wall reflection of the ZnO microcavities. Graphene-induced optical field confinement and lasing emission enhancement were revealed, indicating an energy coupling between graphene SP and ZnO exciton emission. This result demonstrated the response of graphene in the UV wavelength region and extended its potential applications besides many previous reports on the multifunctional graphene/semiconductor hybrid materials and devices in advanced electronics and optoelectronics areas.

Plasmon coupled Fabry-Perot lasing enhancement in graphene/ZnO hybrid microcavity.

The response of graphene surface plasmon (SP) in the ultraviolet (UV) region and the realization of short-wavelength semiconductor lasers not only are two hot research areas of great academic and practical significance, but also are two important issues lacked of good understanding. In this work, a hybrid Fabry-Perot (F-P) microcavity, comprising of monolayer graphene covered ZnO microbelt, was constructed to investigate the fundamental physics of graphene SP and the functional extension of ZnO UV lasing. Through the coupling between graphene SP modes and conventional optical microcavity modes of ZnO, improved F-P lasing performance was realized, including the lowered lasing threshold, the improved lasing quality and the remarkably enhanced lasing intensity. The underlying mechanism of the improved lasing performance was proposed based on theoretical simulation and experimental characterization. The results are helpful to design new types of optic and photoelectronic devices based on SP coupling in graphene/semiconductor hybrid structures.

Rectification behavior of PATP self-assembled on ZnO microrod arrays.

A rectifying hybrid junction was fabricated by the self-assembly of 4-aminothiophenol (PATP) on well-aligned ZnO microrod arrays. Good rectification behavior was obtained from the device of Al/ZnO/PATP/Al. The electron transport at the ZnO/PATP interface was investigated systematically by experimental observation and theoretical simulation. X-ray photoelectron spectroscopy (XPS) analysis confirmed the strong binding between PATP and ZnO via S-Zn bonds. The effective energy barrier and ideality factor of the rectifying diode were estimated by the current-voltage (I-V) measurement and thermionic emission theory. The molecule dipole effect on work function was studied through energy band theory. Theoretical calculation results based on density functional theory (DFT) also indicated a significant dipole, caused by the anchoring effect of PATP, resulting in the changes of surface electronic characteristics of ZnO.

Self-assembled free-standing graphene oxide fibers.

It is a great challenge to directly assemble two-dimensional (2D) graphene oxide (GO) sheets into 1D fibers without any polymer or surfactant for their promising multifunctional applications. Herein, a facile self-assembly strategy is proposed to fabricate neat GO fibers from cost-efficient, aqueous GO suspension at a liquid/air interface based on the repulsive electrostatic forces, attractive van der Waals forces, and π-π stacking. During the self-assembly process and ultrasonic cleaning, the morphology variated from the source graphite powder through GO sheets to GO fibers and finally to neat GO fiber films. It is interesting to note that the electrical property of the GO fiber films was improved dramatically after subsequent low-temperature thermal annealing. The morphological evolution process and formation mechanism were analyzed on the basis of optical microscopy, scanning electron microscopy, and transmission electron microscopy observation, and the electrical characteristics was also discussion.